The present invention relates to sequence network circuits, and more particularly to such circuits for use in protective relaying applications.
The present invention employs the well known theory of symmetrical components. This theory is explained in sustantial detail in the textbook, Symmetrical Components, by Wagner and Evans, published by McGraw-Hill in 1933.
The theory of symmetrical components is widely employed in protective relaying applications. In this connection, see the following U.S. Patents:
U.S. Pat. No. 4,034,269-Wilkinson, issued July 5, 1977; U.S. Pat. No. 4,091,433-Wilkinson, issued May 23, 1978, and U.S. Pat. No. 3,992,651-Hodges, issued Nov. 16, 1976.
One problem with several available sequence network circuits is that such circuits often include an undesirable number of components, such as operational amplifiers and capacitors, which can contribute extraneous transient output signals and increased cost per function. Also, such available circuits can not be conveniently modified to vary the circuit output characteristics as may be necessary when employing such a circuit in different types of protective relaying applications. Further, it would be desirable, for certain protective relaying applications, to provide simple sequence network circuits, such as: quadrature voltage circuits and positive sequence enhancement (positive sequence mix) circuits wherein the input signals to such latter circuits could be either phase-to-neutral or phase-to-phase signals.
Accordingly, it is a general object of this invention to provide sequence network circuits having a small number of components.
It is another object of this invention to provide such sequence network circuits which can be conviently modified for use in different protective relaying applications.
It is another object of this invention to provide such sequence network circuits which include quadrature voltage circuits and positive sequence enhancement circuits.